The present invention relates to pintle-type valves; more particularly, to such valves for variably regulating the flow of fluids and especially gases; and most particularly, to an exhaust gas recirculation (EGR) pintle valve for permitting the controlled admission of exhaust gas into the fuel intake manifold of an internal combustion engine, wherein the valve is provided with an internal flow modifier to change the inherent flow control range of the valve and a head resiliently mounted on a pintle so that the head is self-aligning in a valve seat.
It is well known in the automotive art to provide a variable valve connecting the exhaust manifold with the intake manifold of an internal combustion engine to permit selective and controlled recirculation of a portion of an engine""s exhaust gas into the fuel intake stream. Such recirculation is beneficial for reducing the bum temperature of the fuel mix in the engine to reduce formation of nitrogen and sulfur oxides which are significant components of smog. Such a valve is known in the art as an exhaust gas recirculation (EGR) valve.
A typical prior art EGRpintle-type valve has a valve body enclosing a chamber; a valve seat dividing the chamber between first and second ports; a valve pintle, or stem, extending from the valve head through a bore in a sidewall of the valve body; a valve head fitted to mate with the valve seat and being rigidly attached to and coaxial with the pintle; and a solenoid actuator mounted on the exterior of the valve body and operationally connected to the outer end of the valve pintle, whereby the valve head is axially reciprocated to open and close the valve. The axial stroke of the solenoid may be regulated as by a computer to vary the axial position of the valve pintle and valve head with respect to the valve seat to provide a desired flow volume of fluid through the valve.
Any pintle-type valve has an inherent flow range over which the flow of fluid may be controlled by varying the position of the valve head, from fully closed to wide open. Valves of various size may all have the same relative sensitivity to percent flow variation as a function of pintle motion. However, the sensitivity of control in terms of absolute flow is a function of the size of the valve. Thus, for a wide range of engine sizes, a wide range of EGR valve sizes is presently required. Large engines require large EGR valves, and smaller engines require smaller EGR valves. A large EGR valve on a small engine cannot be controlled with the degree of flow resolution required. If an EGR valve is too small for an engine, then fuel economy and emissions quality can be compromised; if sized too large, then controllability, durability, and performance can be compromised.
Further, the completeness or quality of sealing demonstrated by a known pintle valve depends upon the degree of geometric perfection achieved in the manufacture and assembly of the various components. In many applications, the seat and head are formed of hard metals, which are non-resilient and non-compliant. Therefore, a first requirement is that the seat and head each be perfectly circular so that they can meet to form a seal in an unbroken circular contact line. Fortunately, it is relatively straightforward in the known art to provide a circular seat and head.
A second requirement is that the seat and head be presented to each other in coaxial alignment. This is a much more difficult requirement to meet because the bore in the valve body for the pintle must be not only coaxial with the bore for the seat but must also be absolutely orthogonal to a plane containing the seat. Otherwise, a torque is exerted by the head on the pintle as the head attempts to align itself with the seat. With minimal misalignment, the head may be seated but repeated actuation of the valve may cause rapid wear on the misaligned components and the valve may fail prematurely. With greater misalignment, the valve may simply fail to close.
An added complication in providing a perfectly-sealing valve is that the use conditions of a valve may differ dramatically from the conditions of manufacture and calibration. For example, an EGR valve may be asked to operate flawlessly at 350xc2x0 C. or greater, and at a starting temperature below 0xc2x0 C., from fully open to fully closed. The potential for thermal distortion of various components over this range of temperatures requires careful selection of materials and extremely high-quality machining of components. Thus, the manufacture of such valves can be very costly and time-consuming.
An added source of wear in prior art pintle-type valves is the repeated shock of closing the non-resilient head at full solenoid actuation velocity abruptly against the non-resilient seat. Typically, the seat is formed of extremely hard material, for example, Stellite, the wear being taken by the head.
What is needed is a simple means for allowing a large valve to behave like a smaller valve, so that a single valve can be used over a wide range of engine sizes, thus reducing manufacturing and replacement part complexity and cost. What is further needed is a pintle-type valve wherein the valve head is axially and radially and rotationally movable with respect to the pintle to allow the head to be self-aligning in these dimensions with the seat.
It is the object of the invention to provide a simple, inexpensive means for adapting a single valve configuration to have a plurality of flow ranges, while improving flow resolution.
It is a further object of the invention to save cost and complexity in manufacturing and inventorying EGR valves for internal combustion engines.
It is yet a further object of the invention to provide an improved pintle-type valve wherein the geometric manufacturing requirements and tolerances of the valve body, seat, pintle, and head may be relaxed without compromising the performance characteristics of the valve.
It is a further object of the invention to provide an improved high-performance pintle-type valve which is inexpensive to manufacture.
The present invention is directed to a flow modifier for insertion into the chamber of a large pintle valve to change the apparent flow range of the valve to that of a smaller valve. The flow modifier includes a perforated cup-shaped restrictor disposed within the valve on the valve pintle and sealingly surrounding the valve seat such that all flow through the valve must pass through the passageways in the restrictor. The restrictor is held in place by a compression spring surrounding the pintle. The total open area of the passageways may be varied by varying their number and/or size and is preferably substantially less than the open area of the valve seat. The restrictor thus acts as a flow choke or fixed throttle to reduce the flow range of the valve. The restrictor is simple and inexpensive to fabricate, and different restrictors may be provided as required to size a single large valve having a large inherent flow range to a plurality of applications requiring valves having smaller flow ranges. The invention is especially suited to exhaust gas recirculation valve requirements over a wide range of displacement of internal combustion engines.
A further embodiment of the invention is directed to a pintle-type valve having a valve head resiliently mounted on the internal end of the valve pintle. The head is thus free to move axially and/or radially and/or rotationally with respect to the pintle and seat as directed by the mating surface of the valve seat to effect a seal. The head includes a chamber for receiving the end of the pintle and an inwardly-rolled skirt on the well for articulatably capturing the head onto the pintle. Spring means, such as a coil or leaf spring, is disposed between the head and the pintle in the chamber to keep the head generally aligned with the pintle whilst allowing excursions of the head to mate the head sealably with the valve seat and to absorb the shock of such mating.